Earnings Per Share - Schedule of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Basic earnings per share
Net income from continuing operations	$ 61.5	$ 57.6	$ 125.3	$ 106.0
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.4)	(0.4)
Income before discontinued operations available to common shareholders - Basic	61.3	57.4	124.9	105.6
Income (loss) from discontinued operations, net	(49.7)	0.8	(55.5)	2.5
Amount allocated to nonvested participating shareholders	0.0	0.0	0.0	0.0
Income (loss) from discontinued operations available to common shareholders - Basic	(49.7)	0.8	(55.5)	2.5
Net income	11.8	58.4	69.8	108.5
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.4)	(0.4)
Net income available to common shareholders - Basic	$ 11.6	$ 58.2	$ 69.4	$ 108.1
Average common shares outstanding - Basic	233.0	215.4	232.9	215.3
Earnings per share from continuing operations available to common shareholders - Basic	$ 0.26	$ 0.27	$ 0.53	$ 0.49
Earnings per share from discontinued operations available to common shareholders - Basic	(0.21)	0.00	(0.23)	0.01
Earnings per share - Basic	$ 0.05	$ 0.27	$ 0.30	$ 0.50
Diluted earnings per share
Net income from continuing operations	$ 61.5	$ 57.6	$ 125.3	$ 106.0
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.4)	(0.4)
Income before discontinued operations available to common shareholders - Diluted	61.3	57.4	124.9	105.6
Income (loss) from discontinued operations, net	(49.7)	0.8	(55.5)	2.5
Amount allocated to nonvested participating shareholders	0.0	0.0	0.0	0.0
Income (loss) from discontinued operations available to common shareholders - Diluted	(49.7)	0.8	(55.5)	2.5
Net income	11.8	58.4	69.8	108.5
Amount allocated to nonvested participating shareholders	(0.2)	(0.2)	(0.4)	(0.4)
Net income available to common shareholders - Diluted	$ 11.6	$ 58.2	$ 69.4	$ 108.1
Average common shares outstanding - Basic	233.0	215.4	232.9	215.3
Assumed conversion of stock options, unvested restricted stock and contingent performance shares, net	0.6	0.5	0.6	0.5
Average common shares outstanding - Diluted	233.6	215.9	233.5	215.8
Earnings per share from continuing operations available to common shareholders - Diluted	$ 0.26	$ 0.27	$ 0.53	$ 0.49
Earnings per share from discontinued operations available to common shareholders - Diluted	(0.21)	0.00	(0.23)	0.01
Earnings per share - Diluted	$ 0.05	$ 0.27	$ 0.30	$ 0.50
Anti-dilutive shares	0.4	0.0	0.3	0.0